The invention concerns an arrangement having an electric motor, and in particular having an electronically commutated motor (ECM).
Examples of such motors are shown, for example, in the following documents assigned to the assignee of the present application:
DE 44 41 372 A1=5,845,045 JESKE
EP 0 658 973 B1=5,590,235 JESKE
DE 296 06 939.6-U=EP 0 739 084 A2
DE 195 15 944 A1
EP 0 741 449 A1=6,163,117
EP 0 744 807 B1=5,847,523
DE 195 18 991 A1
DE 196 47 983 A1=6,091,887
EP 0 780 962 A2
It would not be possible to reproduce the extensive content of these documents even in summarized form, and reference is therefore made to their complete contents.
It is an object of the invention to make available a new arrangement and a new method for controlling an electric motor.
According to the invention, this object is achieved by connecting an output signal of a microprocessor, which can take on either a high level or a low level, to a voltage divider which regulates motor current, and varying the microprocessor output signal to achieve a desired motor current characteristic curve. It is possible thereby, in program-controlled fashion, either to extend acceleration (called a xe2x80x9csoft startxe2x80x9d) or to make acceleration as short as possible by raising the operating point for the current control system during the acceleration period so that the motor current can be higher during acceleration than later in normal operation.
A preferred method is to set a motor current limit to a first value for motor startup, to monitor the startup, and to reset the motor current limit to a second value after startup. This method can be flexibly adapted to the needs of a user, since the limiting values can be adjusted in program-controlled fashion.
The invention additionally concerns a method for controlling a physical variable, in particular a rotation speed, having the following steps:
a) in order to ascertain the system deviation, a difference is determined between a desired value for the physical variable (in digital form), and an actual value for the physical variable (also in digital form);
b) the sign and absolute value of that difference are ascertained;
c) an analog memory element is charged or discharged, depending on the sign;
d) the duration of the charging or discharging operation is in each case substantially proportional to the magnitude of the ascertained absolute value of the difference;
e) a value dependent on the charge of the analog memory element is used to influence the pulse duty factor of an actuating member that in turn influences, with its output signal, the physical variable that is to be controlled.
The result is to create a highly advantageous combination of digital accuracy in ascertaining the system deviation, and subsequent processing of that system deviation in order to influence the physical variable.
A further way of achieving the stated object is provided by a method for temperature-dependent control of the rotation speed of an electric motor having the following steps:
a) value clusters of characteristic definition points are stored in a memory, said value clusters containing at least one value characterizing a specific temperature, and one rotation speed datum associated with that temperature;
b) a present value characterizing the temperature that controls the motor rotation speed is sensed at time intervals;
c) that sensed value is compared to the stored values that characterize the temperature and are contained in the stored value clusters;
d) a stored value adjacent to the present value is ascertained;
e) by way of an interpolation proceeding from that adjacent value, a rotation speed datum for the sensed present value is ascertained;
f) a value derived from that interpolated rotation speed datum is conveyed to the electric motor.
It is thereby possible, by storing a small number of value clusters, to define the rotation speed behavior of a motor as a function of temperature.
The invention furthermore concerns a method for A/D conversion in an arrangement having a voltage divider containing a temperature-dependent resistor, one tapping point of that voltage divider defining the potential at the one input of a comparator, and the potential at the other input of the comparator being determined by a capacitor that can be charged via a constant-current source, having the following steps:
a) first the capacitor is discharged;
b) then a measurement is made of the time required for the capacitor, as it is charged by the constant-current source, to reach the potential of the other input;
c) that time is used as an indication of the temperature of the temperature-dependent resistor.
A method of this kind can easily be implemented using a microcontroller which controls or regulates functions of an electric motor. That microcontroller can effect discharge of the capacitor in step a), and can provide time measurement as defined in step c), the overall result being a very simple method.
Another way of achieving the stated object is provided by an electric motor having discrete values, stored in a memory, which (in the form of support values) define a temperature/rotation speed characteristic, the discrete values being modifiable via a data connection to an input device arranged outside the electric motor. This makes possible simple adaptation of such a motor to different customer requirements.
A further way of achieving the stated object concerns a method for operating an electronically commutated motor having associated with it a microprocessor or microcontroller and a program associated therewith, that program serving to control a plurality of motor functions of different priorities, having the following steps:
a) a plurality of requestable routines necessary for operation of the motor are provided;
b) when a requestable routine is needed, a corresponding request signal for it is set;
c) a higher-level program function is used to check which requested routine has the highest priority, and that highest-priority routine is executed first;
d) following execution of that highest-priority routine, the request signal associated with that routine is reset
A method of this kind makes very good use of the available computing capacity of a microprocessor or microcontroller, and makes it possible to repeat specific time critical interrogations or the like at intervals which do not exceed a predefined duration. These can be, for example, interrogations of a data bus by means of which data or instructions can be conveyed to the motor. This method is preferably continuously repeated, in the manner of a loop, while the motor is operating, the loop sequences being different depending on the type of routine requested. It is particularly advantageous in this context if a requestable routine to be executed in the program can in turn generate, during its execution, a request signal for another requestable routine to be executed. This allows close concatenation of routines, between each of which time-critical program steps can be executed.
A further way of achieving the stated object concerns a motor having a microprocessor or microcontroller and a bus, in which the microprocessor or microcontroller controls both the bus and the motor. A motor of this kind is very inexpensive due to the reduction in electronic components, and the elimination of further electronic components moreover makes possible a compact design for the motor. Because the entire control system of the motor is displaced into the microprocessor or microcontroller, it is possible to make changes to the motor merely by changing the software.